The present invention is directed to an improved veno-venous extracorporeal oxygenator, referred to herein as a “paracorporeal respiratory assist lung” or the “PRAL device.” More specifically, the paracorporeal respiratory assist lung includes a variable speed (oscillating) rotating fiber bundle having increased porosity. In addition, the PRAL device may be configured to rotate a core wherein the fiber bundle is stationary, and may further be configured to include a fiber bundle on the rotating core.
It has been reported that 350,000 Americans die of lung disease each year, most from Acute Respiratory Distress Syndrome (ARDS) and Chronic Obstructive Pulmonary Disease (COPD). The most common treatment is mechanical ventilation, but may further exacerbate respiratory insufficiency and can cause serious side effects, such as barotrauma and volutrauma. It has been further reported that heart-lung machines, which utilize oxygenators, are employed during surgery throughout the world hundreds of thousands of times per year. Such oxygenators may be useful in treating COPD and ARDS. However, inefficient mass transfer (gas exchange) of oxygen and carbon dioxide is a common problem in oxygenators used in heart-lung machines.
The use of membrane oxygenators to oxygenate blood is well known in the art. One type of conventional membrane oxygenator employs bundles of hollow fibers retained within a cylindrical housing wherein oxygen is pumped through the hollow fibers in the same direction as the blood. The hollow fibers consist of a microporous membrane which is impermeable to blood and permeable to gas. Gas exchange takes place when venous blood flows through the housing and contacts the hollow fibers. Based on the law of diffusion, the oxygen diffuses across the hollow fiber walls and enriches venous blood in contact with these hollow fibers. A stated disadvantage to this type of membrane oxygenator is that a blood boundary layer is formed around the hollow fibers which retards oxygenation of blood that does not directly contact the hollow fibers.
Another known type of membrane oxygenator includes moving a portion of the oxygenator to provide increased mixing of blood flow. In this type of membrane oxygenator, a blood flow path and an oxygen flow path are positioned between a rotor and a stator and separated by a membrane and a wafer. When the rotor rotates relative to the stator, mixing of blood flow occurs resulting in disruption of the blood boundary layer. Although such an oxygenator provides a degree of mixing of blood, this mixing may cause destruction of red blood cells. In one embodiment of such an oxygenator, a cylindrical, semi-permeable membrane containing oxygen is rotated in a housing such that blood contacts and flows over the membrane and oxygen is transferred through the rotating membrane to the blood. One reported problem with this type of membrane oxygenator is the poor permeability to oxygen and carbon dioxide of semi-permeable membranes.
Yet another known membrane oxygenator includes hollow fiber membranes that extend substantially longitudinally, first inert fibers are spaced between them and also extend substantially longitudinally. Second inert fibers extend generally transverse to the hollow fibers and generally contiguous therewith, so that an oxygen-containing gas can pass through the hollow fibers and blood can be passed over their exterior for gas exchange through the membrane. The second inert fibers may form a weft and the first inert fibers are spaced one between each two hollow fibers so that the warp consists of alternating strands of hollow fiber and first inert fiber passing over the weft in an oscillating fashion. The inert fibers are disclosed as biocompatible monofilament polymers that provide spacing of the hollow fibers to produce even blood films. However, such an oxygenator is not designed for extracorporeal applications having relatively low blood flow rates.
Accordingly, there is a need for, and what was heretofore unavailable, an extracorporeal oxygenator having enhanced gas exchange characteristics resulting from a variable rotating fiber bundle and/or increased porosity of the fiber bundle that has high gas exchange efficiency with minimal damage to the blood components.